mapexpr ( expr ; l )

apply an expression to every value in a value list

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steve harley
paper ape
http://istilldonthaveawebsite.com

Sample input:

mapexpr (
"left (_v; 3)";
list ("abc"; "wxyz"; "ferdinand")
)

Sample output:

"abc
wxy
fer"

Function definition: (Copy & paste into FileMaker's Edit Custom Function window)

/* 
mapexpr (expr, l)

apply an expression to every value in a value list

expr = an expression string suitable for Evaluate() with let variable _v used where each value should be referenced
l = a valuelist (return separated text items)
*/
Let ([
    n = ValueCount (l); 
    lambda = "Let (_v =" & Quote (GetValue (l; 1)) & "; " & expr & ")"
  ];
  Case (
    n=0; "";
    n=1; Evaluate (lambda);
    Evaluate (lambda) & ¶ & mapexpr (expr; RightValues (l; n-1))
  )
)

to perform the same operation on every value in a value list (l), supply an expression (expr) for the operation using "_v" for the value; this custom function will traverses the value list and for each value assigns Let() variable _v to the current value, then uses Evaluate() to apply the expression to the value; the result is a value list with each original value transformed by the expression

notes:
• since mapexpr uses GetValue(), the expression should *not* expect values to be return-terminated
• while value lists are by definition text strings, if the text values are numeric, expr can usually use mathematical operations on each value in the list
• Evaluate() will transform any returns in expr to spaces

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Note: these functions are not guaranteed or supported by BrianDunning.com. Please contact the individual developer with any questions or problems.

mapexpr ( expr ; l )

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